Impact of climate change on sea surface wind in Southeast Asia, from climatological average to extreme events: results from a dynamical downscaling

Southeast Asia (SEA) climate shows a large range of variability scales, from extreme events to interannual variability. Understanding its answer to climate change is of primary scientific and socio-economic importance. IPCC 5th assessment report however pointed the lack of knowledge in regional climate change and its impact in SEA. In particular little is known about the answer of wind to climate change. The impact of climate change on sea surface wind speed is investigated here, examining changes in daily and extreme event scales, interannual variability and climatological average between the twentieth and twenty-first centuries. For that the RegCM4 regional model was used to perform a dynamical downscaling of CMIP5 simulations done with CNRM-CM5 global climate model under RCP4.5 and RCP8.5 hypothesis. Comparisons with QuikSCAT satellite data show that the downscaled simulations perform overall better than the global simulations. Both models produce regionally and seasonally contrasted results in terms of daily wind speed answer to climate change. Global simulations produce mostly weak and non-significant changes, only suggesting an intensification of northeast winter monsoon in the northern SEA. Conversely regional downscaled simulations suggest from March to November in the northern South China Sea and Pacific regions a significant weakening of wind speed from climatological to daily scales (summer monsoon to extreme values), for regions and periods of initially strong values, associated with a 40-50% decrease of tropical cyclones frequency. These changes result from the increase of mean meridional south to north sea level pressure gradient and decrease its daily variability.